The long-term objective of this Program Project is to understand the mutagenic and carcinogenic properties of polycyclic aromatic hydrocarbons (PAH) and related chemical agents at the molecular level. The specific aims of this Project are largely dictated by the conviction that the long- term objective cannot be met without structural identification and determination of both depurinating and stable DNA adducts and detailed data on the repair of DNA damage from these lesions. To this end, the laser- based techniques of fluorescence line narrowing (FLN) and non-line narrowing (NLN) fluorescence spectroscopy are employed. The research proposed has four aims. The first is to use FLN/NLN spectroscopies for identification of DNA adducts formed by 6-methyl-benzo[alpha]pyrene and 5- methylchrysene. These PAH are suitable for further testing of the hypothesis that apurinic sites play an important role in tumor initiation; formation of adducts by the former and latter occurs predominantly by the one-electron oxidation and diolepoxide pathways, respectively. The second aim is to extend our pioneering experimental and computational studies of multiple conformations of diolepoxide adducts from dibenzo[alpha, l]pyrene to benzo[c]phenanthrene and benzo[delta]chrysene, which also possess crowded fjord regions. The molecular conformation of the diolepoxide should influence the mechanistic aspects of binding to DNA, as well as adduct conformations in DNA and repairability. The third aim is to apply our recently developed FLN/NLN method to study the repair of stable adducts from dibenzo[alpha,l]pyrene and dibenzo[alpha,h]pyrene and to investigate repair dependence on adduct conformation (external, base-stacked, or intercalated). We also hope to develop a simple and reliable fluorescence- based method for monitoring the repair of apurinic sites in cells. Apurinic sites would be monitored via DNA single-strand breaks which are detected using the fluorescent probe acridine orange. The fourth aim is the development of a fluorimetric methodology which yields quantitative adduct profiles for PAH. Such profiles would be important for assessing the dependence of adduct heterogeneity on dosage.